feat: introduce codex-utils-cargo-bin as an alternative to assert_cmd::Command (#8496)

This PR introduces a `codex-utils-cargo-bin` utility crate that
wraps/replaces our use of `assert_cmd::Command` and
`escargot::CargoBuild`.

As you can infer from the introduction of `buck_project_root()` in this
PR, I am attempting to make it possible to build Codex under
[Buck2](https://buck2.build) as well as `cargo`. With Buck2, I hope to
achieve faster incremental local builds (largely due to Buck2's
[dice](https://buck2.build/docs/insights_and_knowledge/modern_dice/)
build strategy, as well as benefits from its local build daemon) as well
as faster CI builds if we invest in remote execution and caching.

See
https://buck2.build/docs/getting_started/what_is_buck2/#why-use-buck2-key-advantages
for more details about the performance advantages of Buck2.

Buck2 enforces stronger requirements in terms of build and test
isolation. It discourages assumptions about absolute paths (which is key
to enabling remote execution). Because the `CARGO_BIN_EXE_*` environment
variables that Cargo provides are absolute paths (which
`assert_cmd::Command` reads), this is a problem for Buck2, which is why
we need this `codex-utils-cargo-bin` utility.

My WIP-Buck2 setup sets the `CARGO_BIN_EXE_*` environment variables
passed to a `rust_test()` build rule as relative paths.
`codex-utils-cargo-bin` will resolve these values to absolute paths,
when necessary.


---
[//]: # (BEGIN SAPLING FOOTER)
Stack created with [Sapling](https://sapling-scm.com). Best reviewed
with [ReviewStack](https://reviewstack.dev/openai/codex/pull/8496).
* #8498
* __->__ #8496

Author: bolinfest

AGENTS.md

@@ -77,6 +77,12 @@ If you don’t have the tool:
 - Prefer deep equals comparisons whenever possible. Perform `assert_eq!()` on entire objects, rather than individual fields.
 - Avoid mutating process environment in tests; prefer passing environment-derived flags or dependencies from above.
 
+### Spawning workspace binaries in tests (Cargo vs Buck2)
+
+- Prefer `codex_utils_cargo_bin::cargo_bin("...")` over `assert_cmd::Command::cargo_bin(...)` or `escargot` when tests need to spawn first-party binaries.
+  - Under Buck2, `CARGO_BIN_EXE_*` may be project-relative (e.g. `buck-out/...`), which breaks if a test changes its working directory. `codex_utils_cargo_bin::cargo_bin` resolves to an absolute path first.
+- When locating fixture files under Buck2, avoid `env!("CARGO_MANIFEST_DIR")` (Buck codegen sets it to `"."`). Prefer deriving paths from `codex_utils_cargo_bin::buck_project_root()` when needed.
+
 ### Integration tests (core)
 
 - Prefer the utilities in `core_test_support::responses` when writing end-to-end Codex tests.

codex-rs/Cargo.lock

@@ -36,6 +36,7 @@ members = [
     "tui",
     "tui2",
     "utils/absolute-path",
+    "utils/cargo-bin",
     "utils/git",
     "utils/cache",
     "utils/image",
@@ -93,6 +94,7 @@ codex-tui = { path = "tui" }
 codex-tui2 = { path = "tui2" }
 codex-utils-absolute-path = { path = "utils/absolute-path" }
 codex-utils-cache = { path = "utils/cache" }
+codex-utils-cargo-bin = { path = "utils/cargo-bin" }
 codex-utils-image = { path = "utils/image" }
 codex-utils-json-to-toml = { path = "utils/json-to-toml" }
 codex-utils-pty = { path = "utils/pty" }

codex-rs/Cargo.toml

@@ -48,7 +48,6 @@ uuid = { workspace = true, features = ["serde", "v7"] }
 
 [dev-dependencies]
 app_test_support = { workspace = true }
-assert_cmd = { workspace = true }
 base64 = { workspace = true }
 core_test_support = { workspace = true }
 mcp-types = { workspace = true }

codex-rs/app-server/Cargo.toml

@@ -9,12 +9,12 @@ path = "lib.rs"
 
 [dependencies]
 anyhow = { workspace = true }
-assert_cmd = { workspace = true }
 base64 = { workspace = true }
 chrono = { workspace = true }
 codex-app-server-protocol = { workspace = true }
 codex-core = { workspace = true, features = ["test-support"] }
 codex-protocol = { workspace = true }
+codex-utils-cargo-bin = { workspace = true }
 serde = { workspace = true }
 serde_json = { workspace = true }
 tokio = { workspace = true, features = [

codex-rs/app-server/tests/common/Cargo.toml

@@ -11,7 +11,6 @@ use tokio::process::ChildStdin;
 use tokio::process::ChildStdout;
 
 use anyhow::Context;
-use assert_cmd::prelude::*;
 use codex_app_server_protocol::AddConversationListenerParams;
 use codex_app_server_protocol::ArchiveConversationParams;
 use codex_app_server_protocol::CancelLoginAccountParams;
@@ -49,7 +48,6 @@ use codex_app_server_protocol::ThreadResumeParams;
 use codex_app_server_protocol::ThreadStartParams;
 use codex_app_server_protocol::TurnInterruptParams;
 use codex_app_server_protocol::TurnStartParams;
-use std::process::Command as StdCommand;
 use tokio::process::Command;
 
 pub struct McpProcess {
@@ -78,12 +76,8 @@ impl McpProcess {
         codex_home: &Path,
         env_overrides: &[(&str, Option<&str>)],
     ) -> anyhow::Result<Self> {
-        // Use assert_cmd to locate the binary path and then switch to tokio::process::Command
-        let std_cmd = StdCommand::cargo_bin("codex-app-server")
-            .context("should find binary for codex-mcp-server")?;
-
-        let program = std_cmd.get_program().to_owned();
-
+        let program = codex_utils_cargo_bin::cargo_bin("codex-app-server")
+            .context("should find binary for codex-app-server")?;
         let mut cmd = Command::new(program);
 
         cmd.stdin(Stdio::piped());

codex-rs/app-server/tests/common/mcp_process.rs

@@ -25,5 +25,6 @@ tree-sitter-bash = { workspace = true }
 [dev-dependencies]
 assert_cmd = { workspace = true }
 assert_matches = { workspace = true }
+codex-utils-cargo-bin = { workspace = true }
 pretty_assertions = { workspace = true }
 tempfile = { workspace = true }

codex-rs/apply-patch/Cargo.toml

@@ -1,8 +1,13 @@
-use assert_cmd::prelude::*;
+use assert_cmd::Command;
 use std::fs;
-use std::process::Command;
 use tempfile::tempdir;
 
+fn apply_patch_command() -> anyhow::Result<Command> {
+    Ok(Command::new(codex_utils_cargo_bin::cargo_bin(
+        "apply_patch",
+    )?))
+}
+
 #[test]
 fn test_apply_patch_cli_add_and_update() -> anyhow::Result<()> {
     let tmp = tempdir()?;
@@ -16,8 +21,7 @@ fn test_apply_patch_cli_add_and_update() -> anyhow::Result<()> {
 +hello
 *** End Patch"#
     );
-    Command::cargo_bin("apply_patch")
-        .expect("should find apply_patch binary")
+    apply_patch_command()?
         .arg(add_patch)
         .current_dir(tmp.path())
         .assert()
@@ -34,8 +38,7 @@ fn test_apply_patch_cli_add_and_update() -> anyhow::Result<()> {
 +world
 *** End Patch"#
     );
-    Command::cargo_bin("apply_patch")
-        .expect("should find apply_patch binary")
+    apply_patch_command()?
         .arg(update_patch)
         .current_dir(tmp.path())
         .assert()
@@ -59,10 +62,9 @@ fn test_apply_patch_cli_stdin_add_and_update() -> anyhow::Result<()> {
 +hello
 *** End Patch"#
     );
-    let mut cmd =
-        assert_cmd::Command::cargo_bin("apply_patch").expect("should find apply_patch binary");
-    cmd.current_dir(tmp.path());
-    cmd.write_stdin(add_patch)
+    apply_patch_command()?
+        .current_dir(tmp.path())
+        .write_stdin(add_patch)
         .assert()
         .success()
         .stdout(format!("Success. Updated the following files:\nA {file}\n"));
@@ -77,10 +79,9 @@ fn test_apply_patch_cli_stdin_add_and_update() -> anyhow::Result<()> {
 +world
 *** End Patch"#
     );
-    let mut cmd =
-        assert_cmd::Command::cargo_bin("apply_patch").expect("should find apply_patch binary");
-    cmd.current_dir(tmp.path());
-    cmd.write_stdin(update_patch)
+    apply_patch_command()?
+        .current_dir(tmp.path())
+        .write_stdin(update_patch)
         .assert()
         .success()
         .stdout(format!("Success. Updated the following files:\nM {file}\n"));

codex-rs/apply-patch/tests/suite/cli.rs

@@ -1,4 +1,3 @@
-use assert_cmd::prelude::*;
 use pretty_assertions::assert_eq;
 use std::collections::BTreeMap;
 use std::fs;
@@ -36,7 +35,7 @@ fn run_apply_patch_scenario(dir: &Path) -> anyhow::Result<()> {
     // Run apply_patch in the temporary directory. We intentionally do not assert
     // on the exit status here; the scenarios are specified purely in terms of
     // final filesystem state, which we compare below.
-    Command::cargo_bin("apply_patch")?
+    Command::new(codex_utils_cargo_bin::cargo_bin("apply_patch")?)
         .arg(patch)
         .current_dir(tmp.path())
         .output()?;

codex-rs/apply-patch/tests/suite/scenarios.rs

@@ -5,13 +5,13 @@ use std::path::Path;
 use tempfile::tempdir;
 
 fn run_apply_patch_in_dir(dir: &Path, patch: &str) -> anyhow::Result<assert_cmd::assert::Assert> {
-    let mut cmd = Command::cargo_bin("apply_patch")?;
+    let mut cmd = Command::new(codex_utils_cargo_bin::cargo_bin("apply_patch")?);
     cmd.current_dir(dir);
     Ok(cmd.arg(patch).assert())
 }
 
 fn apply_patch_command(dir: &Path) -> anyhow::Result<Command> {
-    let mut cmd = Command::cargo_bin("apply_patch")?;
+    let mut cmd = Command::new(codex_utils_cargo_bin::cargo_bin("apply_patch")?);
     cmd.current_dir(dir);
     Ok(cmd)
 }